Cellular wireless communications systems, methods and mobile terminals are widely used for voice and/or data communications. As is well known to those having skill in the art, cellular wireless communications systems, methods and mobile terminals include terrestrial cellular wireless communications systems, methods and mobile terminals, and/or satellite cellular wireless communications systems, methods and mobile terminals. As used herein, the term “mobile terminal” includes cellular and/or satellite radiotelephones with or without a multi-line display; Personal Communications System (PCS) terminals that may combine a radiotelephone with data processing, facsimile and/or data communications capabilities; Personal Digital Assistants (PDA) that can include a radio frequency transceiver and a pager, Internet/intranet access, Web browser, organizer, calendar and/or a global positioning system (GPS) receiver; and/or conventional laptop and/or palmtop computers or other appliances, which include a radio frequency transceiver.
It may be desirable, and may be mandatory in the future, that mobile terminals be equipped to determine the geographical location thereof, for example, to support emergency position reporting, often referred to as “E911” position reporting. One way to accomplish this result is to add a GPS receiver to a mobile terminal. As is well known to those having skill in the art, GPS is a satellite navigation system that is funded by and controlled by the U.S. Department of Defense, that provides specially coded satellite signals that can be processed in a GPS receiver, enabling the receiver to compute position, velocity and/or time. A description of the GPS system may be found in the publication entitled Global Positioning System Overview by Peter H. Dana, 1999, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein. As used herein, the term “GPS” also includes other satellite-based systems that can be used to measure positions on the earth, such as GLONASS.
GPS receivers may be expensive, increase mobile terminal size and/or consume the limited amount of battery power that is available to the mobile terminal. Accordingly, techniques have been proposed to integrate some or all of a GPS receiver into a mobile terminal. See, for example, U.S. Pat. No. 6,424,826 to Horton et al. entitled Systems and Methods for Sharing Reference Frequency Signals Within a Wireless Mobile Terminal Between a Wireless Transceiver and a Global Positioning System Receiver; and U.S. Pat. No. 6,097,974 to Camp, Jr. et al. entitled Combined GPS and Wide Bandwidth Radiotelephone Terminals and Methods.
Moreover, it is known that GPS receivers may suffer from latency in achieving a time to first fix, due to the time that it may take for the GPS receiver to download the necessary GPS satellite ephemeris data. Accordingly, systems have been proposed to shorten the time to first fix. See, for example, U.S. Pat. No. 6,415,154 to Wang et al. entitled Method and Apparatus for Communicating Auxilliary Information and Location Information Between a Cellular Telephone Network and a Global Positioning System Receiver for Reducing Code Shift Search Time of the Receiver; U.S. Pat. No. 6,295,023 to Bloebaum entitled Methods, Mobile Stations and Systems for Acquiring Global Positioning System Timing Information; U.S. Pat. No. 6,169,514 to Sullivan entitled Low-Power Satellite-Based Geopositioning System; and U.S. Pat. No. 5,663,734 to Krasner entitled GPS Receiver and Method for Processing GPS Signals.
In-building GPS operation may be particularly challenging, because the GPS receiver may need to overcome an additional 20 dB-25 dB degradation in received signal-to-noise ratio due to in-building attenuation. This may produce a hundred fold or more increase in the GPS signal processing latency time, compared to an outdoor use.